Software simulation of a quantum computer

Question

While we are waiting for our quantum computers, is it possible to write a software simulation of one? I suspect the answer is no, but hope the reasons why not will throw som

Answer 1

Another reason why classical simulation of quantum computation is hard: to keep track you may want to know after each action of a n-qubit gate (n>1) whether the outgoing qubits are entangled or not. This must be calculated classically but is known to be NP-hard.

See here: https://stackoverflow.com/a/23327816/363429